This invention relates generally to dust guards for the support bearings of axle-mounted electric traction motors, and it relates more particularly to an improved dust guard adapted to cover the axial gap between a hub of the wheel of an electrically propelled traction vehicle and the thrust flange of the adjacent motor support axle bearing.
Propulsion of an electric or a diesel-electric locomotive is accomplished by means of a plurality of traction motors mounted on the trucks of the locomotive between the wheels that are attached to opposite ends of the respective axles. Typically such a motor is designed to be supported by or hung from the axle, with its magnetic frame or stator being connected to suitable axle bearings, and one end (the "pinion" end) of the motor rotor is drivingly coupled to the associated wheel set by suitable gearing. Because of their proximity to the road bed of the railroad track, the axle bearings are exposed during operation of the locomotive to a hostile environment of dirt and other undesirable contaminants. Therefore it has been customary in this art to provide dust guards to impede entrance of dirt and other foreign matter into the bearing regions. While the improved dust guard that is disclosed and claimed hereinafter is particularly well suited for use in conjunction with the axle bearing located at the commutator end of a d-c traction motor on a locomotive, it should be understood at the outset that my invention can alternatively be adapted for use in other settings where its attributes are needed.
In a dust guard the material used for sealing the gap between the relatively stationary axle bearing housing and the rotating wheel hub should be resiliently compressible and should have a relatively low coefficient of sliding friction against metal. In addition, the material should not deteriorate in the presence of lubricating oil and should be relatively stable over a wide range of temperatures. One material having all of these desirable characteristics is felt, and because it prevents lubrication loss from within and entrance of dirt, dust, and grit from outside, felt has been widely used as the sealing medium in prior art dust guards.
In one type of prior art dust guard, as illustrated by U.S. Pat. Nos. 2,954,263 and 3,307,885, a felt annulus is held in frictional engagement with the wheel hub surface by means of a metal ring that is either integral with or attached as a unitary part of the thrust flange of the adjacent axle bearing. This approach has certain shortcomings, due partly to dimensional variations between the circumferences of the wheel hub and of the thrust flange. Within predetermined small tolerances, these parts may vary in their outside diameters, or their centerlines may be eccentric, or they may be slightly out of round.
It is also known to use the resilience of an annular elastomeric band to bias the felt annulus into frictional engagement with the wheel hub surface. An advantageous embodiment of this prior art approach is disclosed and claimed in U.S. Pat. No. 3,713,709--Staiger, and the present invention is an improvement of the Staiger dust guard. While the Staiger dust guard has provided satisfactory service, in some applications it has not been as effective as desired with respect to preventing dirt and other foreign particles from working their way under the felt annulus into the axial gap between the rotating wheel hub and the relatively stationary thrust flange of the adjacent axle bearing. Ingress of any dirt is of course undesirable because it can clog the axle lubricating wick of the bearing, thereby reducing the flow of lubricating oil to the bearing interfaces, and because it can cause excessive wear of the thrust flange face, thereby permitting increased end play and vibration of the traction motor.
In the art of oil seals it has heretofore been suggested to increase radial bias or pressure by putting a garter spring around the outside of the sealing annulus (see U.S. Pat. No. 1,383,466--Jett). There are a number of reasons why such an arrangement is not practical in a dust guard for an axle bearing of a locomotive. The spring could be damaged or broken by the impact of loose stones that are dislodged with great force from the road bed under the locomotive. The initial installation of a garter spring on a dust guard, and its later dismantling for maintenance or repair purposes, is not feasible because of the relatively large force required to stretch the spring and because of the very confined space available in the vicinity of the dust guard.
In order to remove an axle bearing or a traction motor from the axle of a locomotive for repair or replacement purposes, the dust guard must first be removed from the thrust flange and later reassembled, and these tasks are made very difficult by the narrow, inaccessible area in which the dust guard is located. Access to the dust guard is limited by the physically bulky parts between which it is located, namely, the locomotive wheel on one side and the traction motor housing and axle bearing cap on the other side.